Conceptual Engineering of CARA Fuel Element with Negative Void Coefficient for Atucha II

Abstract

Experimentally validated void reactivity calculations were used to study the feasibility of a change in the design basis of Atucha II Nuclear Power Plant including the Large LOCA event. The use of CARA fuel element with burnable neutronic absorbers and enriched uranium is proposed instead of the original fuel. The void reactivity, refuelling costs, and power peaking factors are analysed at conceptual level to optimize the burnable neutronic absorber, the enrichment grade, and their distribution inside the fuel. This work concludes that, for the considered plant conditions, either a void reactivity coefficient granting no prompt critical excursion on Large LOCA or negative void reactivity is achievable, with advantages on refuelling cost and linear power density.

Negative power coefficient on PHWRs with CARA fuel

“…The CVR was deeply studied for many years and a previous work applied to the CARA geometry can be found on reference (Lestani et al, 2011a). Some conclusions from that work are of interest for the present study and can be summarized as follows.…”

“…The uncertainty for two neutronic quantities of great importance for PC, as explained in Section 3, were assessed. Void coefficient, the first quantity of interest, was validated against an experimental benchmark of the DCA reactor (KAERI, 2001) and a prediction uncertainty defined by a standard deviation of 150 pcm was obtained, as can be seen on reference (Lestani et al, 2011a). The uncertainty on the fuel temperature coefficient of reactivity, the second quantity of interest, was verificated against a numerical benchmark (Rahnema and Gheorghiu, 1996) and a numeric uncertainty defined by a 26% mean bias was obtained, as can be seen on reference (Lestani et al, 2011b).…”

“…The Atucha II core has been chosen as the base case because its operating conditions are the most demanding in terms of safety and operation compared to Embalse or Atucha I. Regarding to safety, the void coefficient in Atucha II is the biggest due to its larger core (Lestani et al, 2011a), and the fact that the two loops of the primary circuit are connected via the inlet and outlet plenums, as opposed to the CANDU design which has a splitted primary circuit (CNEA, 1979), imposes that the reactivity introduced on Large-LOCA sets the reactor as supercritical prompt. With respect to operation, besides the aforementioned aspect on VC that also affects PC, the lack of fast response systems to measure and modify core power distributions imposes restrictions on the allowed PC (Bell and Glasstone, 1970b, Chapter 9), as will be further explained.…”